The present invention relates to the use of internal combustion engine exhaust in combined cycle power plants. More particularly, the present invention relates to achieving greater system efficiencies by controlling the quality and distribution of exhaust to the boiler space of a typical steam generated electric power plant.
Where power plant design is concerned, efficiency provides a useful measure of system performance. As the power plant converts energy from one form to another, losses are inevitable. Where the designer reduces such losses, or even transforms the by-products or waste of certain processes into available energy sources, the overall efficiency of the system naturally will increase.
It is known in the art that greater efficiencies in power generation may be achieved by recycling internal combustion engine exhaust as secondary combustion gas and as overfire or underfire air in a typical coal-fired steam generated power plant. In U.S. Pat. No. 4,928,635, which is hereby incorporated by reference, such a system is disclosed. One of the objects of that invention was to make the heat energy of the exhaust available to generate steam. Thus, efficiencies were achieved simply by converting what would otherwise be waste energy into productive energy. At that time, it was necessary to raise the temperature of the exhaust in order to produce high quality steam. It was suggested that refiring a blend of exhaust containing about 13% oxygen and preheated air as secondary combustion gas would be a suitable method for achieving that result.
Upon further investigation, it was discovered that greater overall system efficiencies could be achieved by controlling the amount of oxygen at key locations within the burner, and by routing substantially higher proportions of exhaust to the boiler space directly, as opposed to routing it as secondary or higher level combustion gas, thereby lowering the amount of supplementary firing required in the boiler. The total flow of exhaust into the boiler should constitute a higher percentage of the total gas flow into the boiler than had been previously suggested in order to take full advantage of the thermal energy of the exhaust and to avoid introduction into the boiler, at least as much as possible, of lower temperature gases. The method of the present invention reflects that discovery.